There’s materials already from Wikipedia in the sources linking to articles about that position.
https://en.wikipedia.org/wiki/Legal_status_of_fictional_pornography_depicting_minors?wprov=sfti1
There are both reasonings described and the one supporting the regulation links to studies and further opinions.
I suspect there won’t be evidence in the scientific sense for this - it’s a very opinionated field and not a very researched one.
I just note that it was sufficient to align most if not all European ISPs and content hosts that these measures were not unreasonable.